START > CONTROL PANEL > SYSTEM
Choose the Advance tab. Under Startup and Recovery click Settings button.
There is a drop-down box that is labeled "Default operating system"
Click the down-pointing triangle and select the operating system you want to have load every time.
There are 2 check boxes under that drop-down box, uncheck the first one, leave the second one checked.
Now when you start the computer, it will go directly to XP (if that is what you chose in the drop-down box).